In high performance infrared radiation detector arrays, particularly in long wavelength infrared radiation (LWIR) applications (8-12 micrometers), the maximization of the R.sub.o A product of the detectors is an important consideration. In order to maximize the R.sub.o A product it is necessary to cool the detectors below 77 K. At such low temperatures device performance is limited by tunnelling current. In order to reduce this undesirable tunnelling current another conventional approach involves the fabrication of two layer HgCdTe heterojunction photodiodes by a liquid phase epitaxy (LPE) technique, the photodiodes generally having an n-type radiation absorbing base region and a p-type collecting region in intimate contact with the base. However, it has been found that in this type of LPE-grown photodiode that it is difficult to precisely control the relative positions of the metallurgical and the electrical junctions and the grading of these junctions, resulting in a degradation in device performance and a difficulty in achieving a reproducibility of performance.
It is thus one object of the invention to provide an IR responsive photodiode in which components of the dark current are suppressed while permitting the unimpeded flow of photo-generated current.
It is another object of the invention to provide an IR responsive photodiode which is more readily fabricated than conventional LPE grown photodiodes and which provide for a greater reproducibility of performance.
It is another object of the invention to provide an IR responsive photodiode which includes a modulated multi-quantum well structure interposed between the base and collector regions, the structure impeding the flow of components of the dark current while permitting the unimpeded flow of photo-generated current.
It is another object of the invention to provide a HgCdTe IR responsive photodiode having a barrier region comprised of a plurality of CdTe and HgTe layers interposed between the base and collector regions, the thickness of the HgTe layers and, hence, the width of the quantum wells being modulated across the barrier region.